1. Field of the Invention
The present invention relates to a power transmitting apparatus mounted in a hybrid vehicle.
2. Description of Related Art
A hybrid vehicle is a vehicle provided with a plurality of drive force sources for traveling that are based on different power generation principles, the drive force sources including an engine that generates dynamic power by converting thermal energy to kinetic energy, a rotary machine with an energy recovery function, and the like. For example, the hybrid vehicle is a vehicle that is provided with an internal combustion engine such as a gasoline engine and a diesel engine, and a rotary machine such as an electric motor, having an electric generation function, and a hydraulic motor, having an accumulator function, as the drive force source. The hybrid vehicle is a vehicle capable of improving energy efficiency and reducing gas emissions by making use of the respective characteristics of the engine and the rotary machine. An example of invention relating to such a hybrid vehicle is disclosed in Japanese Patent Application Publication No. 2008-120234 (JP 2008-120234 A).
A hybrid drive device disclosed in this JP 2008-120234 A is provided with an engine, a first motor that has a function of generating electricity by dynamic power from the engine, and a second motor that outputs dynamic power to an output member using electric power generated by the first motor. The first motor and the second motor are coaxially arranged and a power split mechanism that distributes the dynamic power output by the engine to the first motor side and the output member side is arranged between the first motor and the second motor. The hybrid drive device disclosed in this JP 2008-120234 A has a transmission gear device that changes speeds of an output torque of the engine and transmits to the power split mechanism arranged between the first motor and the second motor.
Japanese Patent Application Publication No. 2008-265598 (JP 2008-265598 A) discloses an invention relating to a hybrid vehicle provided with an engine, a first motor, a second motor, and a power split mechanism that is configured by a planetary gear unit having three rotation elements. The hybrid vehicle according to JP 2008-265598 A is further provided with a clutch that non-rotatably fixes an output shaft of the engine. The first motor is engaged with the output shaft of the engine via the power split mechanism and the second motor is engaged with drive wheels. Respective operations of the engine, the first motor, the second motor, and the clutch are configured so as to be controlled in accordance with a requested drive force of the vehicle. Further, the vehicle is configured such that when the clutch is engaged to fix the output shaft of the engine, motor traveling mode is possible by driving both the first motor and the second motor, in a state where the power split mechanism is made to function as a speed reduction mechanism or a speed increase mechanism.
A similar configuration as that of the hybrid vehicle described in JP 2008-265598 A is also disclosed in Japanese Patent Application Publication No. 2008-265600 (JP 2008-265600 A). JP 2008-265600 discloses a technology in which, if a clutch is engaged and the condition for non-rotatably fixing a crank shaft of the engine is satisfied, an operation of the engine is stopped and at the same time, rotations of the two motors are controlled respectively using a map that specifies a torque split at which the two motors are driven most efficiently on a basis of accelerator operation amount, vehicle speed, and gear ratio of the transmission gear device.
As the abovementioned hybrid drive device disclosed in JP 2008-120234, by adding a transmission gear mechanism for changing the engine speed to the configuration of the power transmitting apparatus for a hybrid vehicle provided with an engine, an electric motor, and a power split mechanism, the engine can be operated at a speed more advantageous in terms of fuel efficiency in accordance with requested drive forces and traveling states of the vehicle. Moreover, energy efficiency of a hybrid vehicle can be improved.